Dieback of Alpine Ash as Related to Changes in Soil Temperature

Abstract

SUMMARY A widespread mortality of alpine ash, Eucalyptus delegatensis (R.T. Baker), in northern Tasmania is considered to be due to changes in the microclimate of the soil following the invasion of the stands by rainforest understoreys. Measurements made during a period of 2 years showed that healthy stands had mean annual soil temperatures greater than 7°C; beneath unhealthy stands the mean annual soil temperatures were less than 7°C. The soil beneath affected stands was moister in summer than that beneath unaffected stands; this possibly was the result of fog stripping by the microphyllous rainforest understorey. When compared with those of healthy stands, the maximum summer soil temperatures at a depth of 4 inches beneath dead and dying stands were depressed by as much as 8°C, and mean annual temperatures were depressed by about 2°C. Mortality is attributed to the inability of established trees to adapt their root: Crown ratios to accommodate changes of this magnitude.